TUNABLE BIREFRINGENT FILTERS USING LIQUID CRYSTAL ELEMENTS

RECENT ADVANCES IN LIQUID CRYSTAL TECHNOLOGY MAKE IT POSSIBLE TO CONSTRUCT TUNABLE BIREFRINGENT FILTERS OPERATINGOVER THE RANGE 3,500-20,000 ANGSTROMS, WITH PASSBANDS AS NARROW AS 50 ANGSTROMS. THE CENTER WAVE-LENGTH OF THIS FILTER CAN BE SELECTED ELECTRONICALLY, IN A FEW MILLISECONDS, WITH NO MOVING PARTS. THESE FILTERS SHOULD BERELATIVELY INEXPENSIVE TO PRODUCE ($1K-2K). THE RESEARCHERSPROPOSE DEVELOPING THESE MODERATE-PASSBAND FILTERS FOR ASTRONOMICAL USES, INCLUDING BROAD-BAND PHOTOMETRY. RAPIDLYTUNABLE FABRY-PEROT ETALONS CAN ALSO BE BUILT USING THE SAMETECHNOLOGY. THE PASSBAND IS TUNED BY ADJUSTING THE VOLTAGE ACROSS A LIQUID CRYSTAL SLAB. THE CENTER WAVELENGTHIS MONITORED BY A REFERENCE LASER DIODE, USED TO STABILIZE THE ETALON UNDER SERVO CONTROL. PLACING THESE ELEMENTS IN SERIES PRODUCES A "HYBRID" TUNABLE FILTER WITH HIGH TRANSMISSION AND A FULL-WIDTH AT HALF-MAXIMUM OF APPROXIMATELY 1 ANGSTROM. THIS HYBRID FILTER HAS APPLICATIONS IN SOLAR AND STELLAR ASTRONOMY, AND IS PARTICULARLY ATTRACTIVE COMPARED TO PRESENTLY-AVAILABLE TUNABLE FILTERS, WHICH ARE VERY EXPENSIVE ($100K). THEY PROPOSE TO MODEL THE PROPERTIES OF BIREFRINGENT FILTERS AND FABRY-PEROT ETALONS, BASED ON MEASUREMENTS OF INDIVIDUAL LIQUID CRYSTAL ELEMENTS, AND TO IDENTIFY SUITABLE OBSERVING PROGRAMS FOR TESTING THE FILTER.